/* ===========================================================
 * docsify sw.js
 * ===========================================================
 * Copyright 2016 @huxpro
 * Licensed under Apache 2.0
 * Register service worker.
 * ========================================================== */

const RUNTIME = "docsify";
const HOSTNAME_WHITELIST = [
    self.location.hostname,
    "fonts.gstatic.com",
    "fonts.googleapis.com",
    "unpkg.com"
];

// The Util Function to hack URLs of intercepted requests
const getFixedUrl = req => {
    var now = Date.now();
    var url = new URL(req.url);

    // 1. fixed http URL
    // Just keep syncing with location.protocol
    // fetch(httpURL) belongs to active mixed content.
    // And fetch(httpRequest) is not supported yet.
    url.protocol = self.location.protocol;

    // 2. add query for caching-busting.
    // Github Pages served with Cache-Control: max-age=600
    // max-age on mutable content is error-prone, with SW life of bugs can even extend.
    // Until cache mode of Fetch API landed, we have to workaround cache-busting with query string.
    // Cache-Control-Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=453190
    if (url.hostname === self.location.hostname) {
        url.search += (url.search ? "&" : "?") + "cache-bust=" + now;
    }
    return url.href;
};

/**
 *  @Lifecycle Activate
 *  New one activated when old isnt being used.
 *
 *  waitUntil(): activating ====> activated
 */
self.addEventListener("activate", event => {
    event.waitUntil(self.clients.claim());
});

/**
 *  @Functional Fetch
 *  All network requests are being intercepted here.
 *
 *  void respondWith(Promise<Response> r)
 */
self.addEventListener("fetch", event => {
    // Skip some of cross-origin requests, like those for Google Analytics.
    if (HOSTNAME_WHITELIST.indexOf(new URL(event.request.url).hostname) > -1) {
        // Stale-while-revalidate
        // similar to HTTP's stale-while-revalidate: https://www.mnot.net/blog/2007/12/12/stale
        // Upgrade from Jake's to Surma's: https://gist.github.com/surma/eb441223daaedf880801ad80006389f1
        const cached = caches.match(event.request);
        const fixedUrl = getFixedUrl(event.request);
        const fetched = fetch(fixedUrl, { cache: "no-store" });
        const fetchedCopy = fetched.then(resp => resp.clone());

        // Call respondWith() with whatever we get first.
        // If the fetch fails (e.g disconnected), wait for the cache.
        // If there’s nothing in cache, wait for the fetch.
        // If neither yields a response, return offline pages.
        event.respondWith(
            Promise.race([fetched.catch(_ => cached), cached])
                .then(resp => resp || fetched)
                .catch(_ => {
                    /* eat any errors */
                })
        );

        // Update the cache with the version we fetched (only for ok status)
        event.waitUntil(
            Promise.all([fetchedCopy, caches.open(RUNTIME)])
                .then(
                    ([response, cache]) =>
                        response.ok && cache.put(event.request, response)
                )
                .catch(_ => {
                    /* eat any errors */
                })
        );
    }
});
